During a typical MOCVD growth process, a wafer substrate may be directly placed on a susceptor in an MOCVD growth chamber. The susceptor, which can be mounted on a rotating shaft, provides support for the wafer substrate during the epitaxial growth of semiconductor layers thereon, while protecting the back side of the wafer. In this environment, epitaxially grown semiconductor layers require precise control of fabrication process parameters so as to reduce operation and process variations and improve the quality, performance and yield of the epitaxially grown semiconductor layers. For example, the uniformity of the temperature over the wafer substrate during a MOCVD growth process is one parameter that requires control.
Thermal uniformity of the wafer substrate during MOCVD growth processing is important, especially for epitaxially grown semiconductor materials such as group III nitride semiconductors that are frequently used in microprocessors, memory integrated circuits and other high density devices. A non-uniform temperature distribution on an epitaxially grown semiconductor layer may generate different chemical reaction rates at different portions of the epitaxially grown semiconductor layers on the wafer substrate. As a result, the material composition of the epitaxially grown semiconductor layers and the deposition rate of the layers may be altered by temperature inhomogeneities arising from the non-uniform temperature distribution. This can cause the epitaxially grown semiconductor layers to be non-uniform across the wafer substrate. In extreme cases, the wafer substrate can bow enough to crack or break, damaging or ruining the epitaxially grown semiconductor layers.
Heating sources, such as inductive heating coils, resistive heating coils or lamps, are commonly employed as a heating source to heat a wafer substrate supported by a susceptor to a predetermined temperature set point during a typical MOCVD growth process. However, it is difficult to precisely control the temperature distribution imparted from these heating sources onto the wafer substrate. Quite often, the temperature distribution generated from these heating sources can be different from a target temperature specified for the MOCVD growth process. This can lead to epitaxially grown semiconductor layers having a non-uniform temperature distribution which can damage or ruin the grown semiconductor layers.